docs: def _to_bel_lines_footer(graph) -> Iterable[str]:
      """Iterate the lines of a BEL graph's corresponding BEL script's footer.
  
      :param pybel.BELGraph graph: A BEL graph
      """
      unqualified_edges_to_serialize = [
          (u, v, d)
          for u, v, d in graph.edges(data=True)
          if d[RELATION] in UNQUALIFIED_EDGES and EVIDENCE not in d
      ]
  
      isolated_nodes_to_serialize = [
          node
          for node in graph
          if not graph.pred[node] and not graph.succ[node]
      ]
  
      if unqualified_edges_to_serialize or isolated_nodes_to_serialize:
          yield '###############################################\n'
          yield 'SET Citation = {"PubMed","Added by PyBEL","29048466"}'
          yield 'SET SupportingText = "{}"'.format(PYBEL_AUTOEVIDENCE)
  
          for u, v, data in unqualified_edges_to_serialize:
              yield '{} {} {}'.format(u.as_bel(), data[RELATION], v.as_bel())
  
          for node in isolated_nodes_to_serialize:
              yield node.as_bel()
  
          yield 'UNSET SupportingText'
          yield 'UNSET Citation'